This invention relates, in general, to semiconductor devices, and more particularly, to Radio Frequency (RF) semiconductor devices having a low source inductance.
RF power devices are used in communication applications, for example, as amplifiers in output stages of transmitters in cellular radios. RF amplifiers are used in a grounded source configuration. In typical RF power devices, the back side of the die is usually the drain of the device. It would be desirable to have the source be the back of the die because it can be easily grounded to a heatsink. This configuration is also desirable because heat may be conducted away by the heatsink. If the back side of the die is the drain, the die must be mounted on beryllium oxide or another insulator to separate the drain from the grounded heatsink. If the back side of the die is the source, then the die may be directly mounted to the heatsink or other groundplane. This would eliminate the use of beryllium oxide, which is expensive and highly toxic.
An RF power device having a back side source has been fabricated. In this device, electrical contact is made to a multitude of source regions on the top side of the die using a single metal interconnect layer. This metal interconnect layer connects the multitude of source regions to a single P+ region which is in contact with the substrate, or the back-side of the die. Although the back side source contact is advantageous, this particular configuration results in high source inductance, which means that the device will exhibit a lower gain. Thus, it would be desirable to fabricate an RF power device that has a low source inductance. In addition, this device requires the use of a double layer metal process. A separate metal layer is required to make electrical contact to the gate and the drain of the device. It would be desirable, in order to simplify and lessen the cost of manufacturing, to fabricate an RF power device having a back-side source, but with a single layer metal process.